Koen Clays - Academia.edu (original) (raw)

Papers by Koen Clays

Proceedings of SPIE, Jun 1, 2012

ABSTRACT This manuscript reports that conjugated polymers can show a significant hyperpolarizabil... more ABSTRACT This manuscript reports that conjugated polymers can show a significant hyperpolarizability, as measured by hyper- Rayleigh scattering (HRS). First, a disubstituted poly(phenanthrene) is examined. It is shown that the polymer exhibits an unexpected, but extremely large second-order nonlinear optical (NLO) response, which moreover strongly depends on the solvent conditions. As the molecular structure of the polymer does not at all fit into the classical paradigms, but yet an extremely high hyperpolarizability is measured, these observations put these theories into perspective. An explanation is postulated, which is based on the variation of the conjugation. Second, the hyperpolarizability of regioregular HTcoupled poly(3-hexylthiophene)s (HT-P3HT)s is measured. It is found that also this conjugated polymer shows a significant hyperpolarizability, showing that the observed NLO behavior of conjugated polymers is not restricted to one polymer, but is instead more general. The dependency of the hyperpolarizability on the degree of polymerization is established.

Angewandte Chemie International Edition

Materials Advances

Push–pull chromophores exhibit useful electro-optic (EO) properties that have the potential to si... more Push–pull chromophores exhibit useful electro-optic (EO) properties that have the potential to significantly improve non-linear EO applications ranging from telecommunications to quantum informatics.

Materials Horizons, 2021

By tuning donor strength, we produce an organic electro-optic chromophore with high hyperpolariza... more By tuning donor strength, we produce an organic electro-optic chromophore with high hyperpolarizability, low absorption, and excellent electro-optic activity, which is demonstrated in a plasmonic–organic hybrid modulator with near record lowVπL.

ABSTRACTThe incorporation of functional nanoparticles in scaffolds for tissue constructs has led ... more ABSTRACTThe incorporation of functional nanoparticles in scaffolds for tissue constructs has led to the creation of artificial extracellular matrices that more accurately mimic the cues present in the native microenvironment of developing tissue. Additionally, light-sensitive inorganic nanoparticles can act as cell biosensors and report on the physiological parameters during tissue growth and organization. In this work, we functionalized collagen nanofibers with semiconductor quantum dots (QDs) and thereby created artificial extracellular matrices that can optically report on cardiomyocyte activity based on QD two-photon fluorescence. We have applied these optically-addressable nanofiber matrices to monitor activities of primary cardiomyocytes and compared the optical responses with patch-clamp data. Combining the long-term stability of QD fluorescence with the deeper light penetration depths achievable through multiphoton imaging, this approach can be used for continuous monitoring...

Communications Chemistry, 2019

Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular a... more Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular aggregates upon lowering the solvent quality. This supramolecular organization largely determines the optical and electronic properties of these polymers. However, despite numerous studies the exact mechanism and kinetics of the aggregation process and the role of external stimuli are still poorly understood. Classical characterization techniques such as electronic spectroscopy, dynamic light scattering, and diffraction-based techniques have not been able to provide a full understanding. Here we use second-harmonic scattering (SHS) and third-harmonic scattering (THS) techniques to investigate this supramolecular aggregation mechanism. Our results indicate that the actual supramolecular aggregation is preceded by the formation of structured polymer-solvent clusters consistent with a nonclassical crystallization pathway.

ChemPlusChem, 2018

The syntheses of oligo(p‐phenylene ethynylene)s (OPEs) end‐functionalized by a nitro acceptor gro... more The syntheses of oligo(p‐phenylene ethynylene)s (OPEs) end‐functionalized by a nitro acceptor group and with a ligated ruthenium unit at varying locations in the OPE chain, namely, trans‐[Ru{(C≡C‐1,4‐C6H4)nNO2}(C≡CR)(dppe)2] (dppe=1,2‐bis(diphenylphosphino)ethane; n=1, R=1,4‐C6H4C≡C‐1,4‐C6H4C≡CPh, 1,4‐C6H4NEt2; n=2, R=Ph, 1,4‐C6H4C≡CPh, 1,4‐C6H4C≡C‐1,4‐C6H4C≡CPh, 1,4‐C6H4NO2, 1,4‐C6H4NEt2; n=3, R=Ph, 1,4‐C6H4C≡CPh), are reported. Their electrochemical properties were assessed by cyclic voltammetry, their linear optical properties and quadratic and cubic nonlinear optical properties were assayed by UV/Vis/NIR spectroscopy, hyper‐Rayleigh scattering studies employing nanosecond pulses at 1064 nm, and broad spectral range Z‐scan studies employing femtosecond pulses, respectively, and their linear optical properties and vibrational spectroscopic behavior in the formally RuIII state was examined by UV/Vis/NIR and IR spectroelectrochemistry, respectively. The potentials of the metal‐local...

ChemPhysChem, 2019

Gold nanoparticles (AuNPs) are regarded as promising building blocks in functional nanomaterials ... more Gold nanoparticles (AuNPs) are regarded as promising building blocks in functional nanomaterials for sensing, drug delivery and catalysis. One remarkable property of these particles is the localized surface plasmon resonance (LSPR), which gives rise to augmented optical properties through local field enhancement. LSPR also influences the nonlinear optical properties of metal NPs (MNPs) making them potentially interesting candidates for fast, high resolution nonlinear optical imaging. In this work we characterize and discuss the wavelength dependence of the hyper‐Rayleigh scattering (HRS) behavior of spherical gold nanoparticles (GNP) and gold nanorods (GNR) in solution, from 850 nm up to 1300 nm, covering the near‐infrared (NIR) window relevant for deep tissue imaging. The high‐resolution spectral data allows discriminating between HRS and two photon photoluminescence contributions. Upon particle aggregation, we measured very large enhancements (ca. 104) of the HRS intensity in the ...

Journal of Organometallic Chemistry, 2018

This paper is dedicated to Professor Irina P. Beletskaya in recognition of her great and innovati... more This paper is dedicated to Professor Irina P. Beletskaya in recognition of her great and innovative research in the field of metal mediated and catalyzed organic synthesis; thank you for your friendship and many inspiring discussions. Happy birthday!

Chemistry – A European Journal, 2018

Analytical Chemistry, 2017

Organic materials are promising candidates for integration in optical network components allowing... more Organic materials are promising candidates for integration in optical network components allowing fast communication. Ultimate speeds can be obtained by exploiting third-order nonlinear optical light-matter interactions that ultimately rely on the molecular second hyperpolarizability (γ). The exploration of molecular structure-property relations is crucial to optimize γ, but requires state of the art measurement techniques which are both sensitive and efficient. Unfortunately, present-day methods for probing the performance of third-order nonlinear optical (NLO) materials fail to meet at least one of those requirements. We have developed third-harmonic scattering (THS) as an alternative method to measure γ in solution, featuring a simple experimental setup and straightforward data analysis. Since the signal strength relies on |γ| 2 , the method proves to be very sensitive and allows rapid screening of organic molecules in dilute solutions for potential use in third-order NLO applications. In this manuscript, we demonstrate the experimental procedure and calibration of THS and have determined the second hyperpolarizability |γ| of commonly used solvents, which can be used as an internal calibration standard. As a proof of concept we determined γ of trans-stilbene, and found it to be in excellent agreement with values obtained by other techniques.

Angewandte Chemie International Edition, 2017

Design of organic noncentrosymmetric materials remains the Holy Grail in the field of second-orde... more Design of organic noncentrosymmetric materials remains the Holy Grail in the field of second-order nonlinear optics. Unlike inorganic crystals currently used in second-order nonlinear optical applications, organic materials represent an attractive alternative due to their

Langmuir : the ACS journal of surfaces and colloids, May 21, 2017

Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refract... more Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confine and concentrate water-soluble analytes. We report a strategy to realize real-time ultrasensitive fluorescence detection in patterned HSCPCs based on strongly enhanced fluorescence due to the photonic band edge effect combined with wettability differentiation in the superhydrophobic/superhydrophilic pattern. The orthogonal nature of the two strategies allows for a multiplicative effect, resulting in an increase of fluorescence of two orders of magnitude.

ACS Photonics, 2016

Up to now colloidal photonic crystal (CPC) lasers essentially relied on photonic band gap edge ef... more Up to now colloidal photonic crystal (CPC) lasers essentially relied on photonic band gap edge effects, as a consequence of the poor passband quality achieved by previously reported engineering methods. In this paper, we demonstrate lasing oscillation in CPC based on the defect mode passband effect. As defect mode, we introduce a high quality monolayer of silica spheres internally functionalized with laser dyes in a sandwiched CPC structure. This defect layer contains the gain medium for lasing action and at the same time breaks the translational symmetry of the crystal, resulting in a pronounced passband within the photonic bandgap. The CPC acts as an optical resonator, effectively insuring the feedback mechanism. The spectroscopic measurements and theoretical simulations match well and reveal that the relatively low-threshold lasing exhibited by the structure can uniquely be attributed to the efficient coupling of the spontaneous emission of the dye to the defect mode of the CPC. Our work provides a new promising strategy towards applications of functionalized self-assembled CPC with a planar defect in all-optical switching, optoelectronics and energy-harvesting, and even in the future generation of electro-optical devices, such as lab-on-a-chip with all-integrated optical spectroscopy techniques.

The Journal of Physical Chemistry C, 2017

The molecular first hyperpolarizability (β) of bacteriorhodopsin is measured over a broad spectra... more The molecular first hyperpolarizability (β) of bacteriorhodopsin is measured over a broad spectral range (800-1300 nm) by means of a spectral hyper-Rayleigh scattering setup. We observe that two photon fluorescence introduces a systematic error towards overestimating the β value. Spectrally resolved hyper-Rayleigh scattering allowed us to quantify and correct for this effect, resulting in a drop to about half of the β value reported in literature. Moreover, we determined the dispersion of β over the wavelength range between 800 and 1300 nm. Applications such as second harmonic generation (SHG) imaging rely on accurate molecular first hyperpolarizability values along with information about resonance effects and wavelength dependent photo-damage. With new and more accurate measurement setups, we can gain more insights in the nonlinear optical response of bacteriorhodopsin.

SPIE Proceedings, 2016

Present-day methods for determining the performance of third-order nonlinear optical materials in... more Present-day methods for determining the performance of third-order nonlinear optical materials include Z-scan, degenerate four-wave mixing and third-harmonic generation (THG). All these techniques possess severe drawbacks; for example, in THG, since all media (air and glass walls of the cell) present a third-order effect, eliminating these contributions requires careful, complex analysis or use of vacuum chambers. We have developed nonlinear scattering as a sensitive, straightforward technique for determining the second hyperpolarizability of samples in solution. Herein, we will for the first time show the applicability of the technique to measure organometallic Ru-complexes, optimized for high nonlinear responses. The investigated compounds showed a significant second hyperpolarizability | |, ranging from 1.1 for the least efficient to 2.8 • 10 esu for the most efficient molecule, and comparable to fullerene C 60 in thin films. It was deemed infeasible to extract hyperpolarizabilities using a high-frequency femtosecond laser source by a modified z-scan setup, which, in contrast to nonlinear scattering, could not account for the high degree of thermal lensing present in the investigated compounds.

Journal of Porphyrins and Phthalocyanines, 2016

Three zwitterionic meso-substituted A3B- and AB2C-porphyrins containing one sulfonato alkylpyridi... more Three zwitterionic meso-substituted A3B- and AB2C-porphyrins containing one sulfonato alkylpyridinium substituent and three or two alkoxy-substituted phenyl groups were synthesized in good yield and fully characterized as to their physicochemical properties by a variety of techniques. This new series of inner salt donor-acceptor meso-substituted porphyrin derivatives were prepared for possible application as amphiphilic probes for membrane insertion in the area of combined second-harmonic and two-photon fluorescence cellular microscopy. To this end, the linear and nonlinear optical properties of the compounds were characterized, together with their electrochemical and spectroelectrochemical properties in non-aqueous media. The neutral design of such molecules enabled us to determine their second order non-linear properties, both by Electric Field Induced Second Harmonic Generation and Hyper–Rayleigh Scattering. Two-photon absorption cross sections of these dyes were also measured by...

Advanced Materials Interfaces, 2016